This invention relates to blind nut fastening methods for fastening blind nuts, to an object article as well as to the blind nuts and tools in use for working said methods.
A prior art blind nut 10, as shown in FIG. 1, includes a tubular body 11 in a uniform outer diameter, a flanged head portion 12, an inner bore 13, and a female thread portion 14 in a smaller diameter than the rest of said bore 13.
Blind nut 10 is made to engage with a lower end of a fastening tool 20 as shown in FIG. 2, then set in a lower aperture 31 of an object article 30 made by thin plate, and operated for fastening as shown FIG. 3.
This fastening tool 20 is also conventional and includes a sleeve 21 with a thrust surface 22 normal to the axial direction, and a spindle 23 independently rotatably disposed through said sleeve 21. The lower portion of spindle 23, projecting from the lower end of sleeve 21, is provided with a male thread bit 24, which is sufficiently longer than female thread portion 14 of blind nut 10.
Prior to insertion of blind nut 10 into lower aperture 31, fastening tool 20 is used such that thread bit 24 is meshed with female thread portion 14 of blind nut 10, so that the lower portion of spindle 23 can be fitted. As the result, the upper surface of head portion 12 is attached on lower thrust surface 22 of sleeve 21. Next, blind nut 10 in couplement with spindle 23 is inserted into a lower aperture 31 of the object article 30, when the lower surface of the head portion is seated on the upper surface of a lower aperture surrounding portion. The inner diameter of lower aperture 31 is slightly larger than the outer diameter of tubular body 11 of blind nut 10, thereby to facilitate insertion of blind nut 10 into aperture 31. As the result, when blind nut 10 is inserted into aperture 31, a slight gap is produced between the neck portion 15 adjacent to head portion 12 of blind nut 10 and the inner peripheral side of lower aperture 31.
After blind nut 10 is set as in the foregoing, spindle 23 independently of fastening tool 20 is rotated in arrow direction A such that male thread bit 24 can be downwards directed along female thread portion 14.
In order for blind nut 10 not to turn together with spindle 23 by torque transferred to tubular body 11 by means of female thread portion 14 and male thread bit 24, head portion 12 is axially pressed with thrush surface 22 of sleeve 21. At this time, the portion provided with female thread portion 14 of tubular body 11 of blind nut 10 is strongly pulled by thread bit 24 in the arrow direction B in FIG. 3, i.e. in the direction of the head portion 12, so that the portion not provided with female thread portion 14 of tubular body 11 may be plastic deformed in a direction of enlarging its diameter as is well known and further bent radially and expanded outwards to produce a flanged and expanding portion 16. As the result, the aperture surrounding portion of the object article 31 is sandwiched by head portion 12 and expanding portion 16 from above and below to thereby fasten blind nut 10 to object article 30. Fastening tool 20 once used to complete fastening of blind nut 10 to object article 30 is removed by rotating spindle 23 in the direction counter to arrow A and disengaging thread bit 24 from female thread portion 14. The so coupled blind nut 10 provides female thread portion 14 useful for a not shown bolt or the like. With respect to blind nut 10 as conventional, the upper half portion of tubular body 11, which portion is not provided with female thread portion 14, is uniform in thickness up to head portion 15. No matter how the head portion is i.e. flat or countersunk, its upper surface is plane normal to the axial direction. On the other hands, sleeve 21 of fastening tool 20 at a time of fastening operation is only operable to press axially the upper surface of head portion 12 with lower thrust surface 22 but not operable to work out in the direction normal to the axial direction, i.e. in the radial and outer direction. Moreover, since the outer diameter of spindle 23 is equal to the one of thread bit 24 or slightly larger and smaller than the inner bore 13 of tubular body 11, spindle 23 in couplement with blind nut 10 produces a gap 17 between its side and tubular body 11 as shown in FIG. 2. It is therefore noted that the part not provided with female thread portion 14 of tubular body 11 of the coupled blind nut 10 is restricted by thrust surface 22 of sleeve 21 and thread bit 24 of spindle 23 with respect to the axial direction but is in not restricted conditions as to the radial direction. Neck portion 15 is also in the same condition.
As the result, when thread bit 24 affords tubular body 11 an axial compressive load, specifically this load is added to female thread 14 in the interior of tubular body 11, the part not provided with female thread portion 14 is deformed excepting neck portion 15 in the radial and outer direction as shown in FIG. 3 to produce expanding portion 16. In contrast, neck portion 15 is deformed in the radial and inner direction to become a changed neck portion 15' in minor diameter. In the result, a slight gap 32 once produced from the inner peripheral side of lower aperture 31 is changed to a wider gap 32'. Fastening strength of blind nut 10 to object article 30, which is in a state of producing wider gap 32', specifically in respect of its turning direction, is provided in that the aperture surrounding portion is sandwiched by head portion 12 and expanding portion 16 under pressure. A degree of its strength depends on the pressure exerted therebetween. Deformed neck portion 15' acts only to connect head portion 12 with expanding portion 16 and is completely detached from the inner peripheral side of lower aperture 31, so that no production of sliding frictional resistance as well as of fastening strength with respect to the turning direction can be expected.
As in the foregoing, since it is very difficult to get sufficiently large fastening strength with respect to the turning direction of the coupled blind nut 10 against object article 30, when torque is given for a bolt to be screwed, there is a fear that both will jointly turn in many cases. In some cases where formation of expanding portion 16 is not satisfactory, it is difficult to fasten any bolt.
As settlement of the foregoing problem, it is known to propose that the lower surface of head portion 12 be radially pleated or the outer peripheral side of neck portion 15 be serrated. In the former case, when torque is given, head portion 12 is sometimes slipped slightly from the aperture surrounding portion and fastening strength in the turning direction can not be enhanced so much as expected. In the latter case, the neck portion is deformed as shown in FIG. 3 and detached from the inner peripheral side of aperture 31, improvement of the fastening strength can hardly be expected from the beginning.
In view of the foregoing problem, it is the major object of this invention to improve largely the fastening effect of a blind nut to an object article, particularly with respect to the turning direction. Accordingly, it is a first object of this invention to provide blind nut fastening methods by extending and deforming the neck portion of a blind nut in the radial and outer direction at fastening times.
It is a second object of this invention to provide a blind nut having the neck portion in a smaller thickness than the other part, thereby facilitating extension and deformation of the neck portion in the radial and outer direction.
It is, further, a third object of this invention to provide fastening tools having the lower end of a sleeve conically formed for advancing forcedly along the neck portion of a blind nut.